An excavator is a type of engineering machine that is mainly used for moving earth or loads, digging work and demolition. An excavator, such as a digging machine, usually comprises a drive unit that comprises an undercarriage and an overcarriage, whereby the overcarriage has a motor and cabin part that can be rotated in relation to the undercarriage. Excavators also comprise an assembly that includes an excavator tool, such as a blade, a shovel, a hook for breaking up frozen ground, an asphalt cutter or a gripping tool, that is attached to the excavator's underbody via a mounting device, and that is usually hydraulically controlled using at least a hydraulically maneuvered lift arm.
When excavating broken rock in mines with an excavator blade for example, the ground can be hard and rough and this means that large forces are required to move the excavator blade forwards. However, if one allows the excavator blade to move up and down in the vertical plane and follow the underlying surface contours the excavator blade becomes easier to move forwards. At the same time the ground becomes more scraped clean and the forces on the blade mounting device will be lower.
Blade oscillation has been used in many applications; usually the excavator blade is pivotably mounted on a shaft that extends in the excavator's forward driving direction. The excavator blade oscillates from side to side around the shaft and the compressive force, i.e. the force that moves the excavator blade forwards, is taken up by slide rails that are arranged on the shaft's periphery and the excavator blade's shaft attachment. A drawback with this construction is that the slide rails provide further resistance to the movement of the excavator blade due to frictional forces in the slide rails and the resistance to oscillate the blade thereby becomes larger in proportion to the compressive force.
Another way of achieving blade oscillation is to make the blade mounting flexible. If the blade mounting is flexible, it is twisted as the blade oscillates. There is then a great risk of fatigue damage to the excavator structure.